1. Technical Field
The present inventions relate to power regulator circuits and, more particularly, relate to regulators that use pass devices.
2. Description of the Related Art
In many implementations, it is often advantageous to have a power regulator that can use either an external pass device or an internal pass device as part of the general regulator topology. The pass device is that device in a series (as distinct from shunt) regulator that passes current from the power source to the load. Use of an external pass device is generally done to place most of the power dissipation on the external pass device, rather than entirely with the remainder of the regulator, which may be on an integrated circuit (IC). The integrated circuit may or may not have other significant power dissipation sources, so thermal management may be a system concern. An internal pass device is usually selected when power dissipation is not a concern, and the area and cost of the external pass device may be avoided. The topology of a series regulator using a series pass transistor for a pass device whose low impedance terminals couple a source of power to a load and whose high impedance terminal couples to an error amplifier that increases difference between an output, which may or may not be scaled, and a reference signal is known.
It has been common for prior integrated circuits to connect via a bus to a system controller to direct a portion of the startup sequence for the power regulators. This was commonly used for startup of an integrated circuit such as MC13783, manufactured and sold by Freescale, Inc. The MC13783 integrated circuit contained dozens of functional circuits such as an audio amplifier and microphone system, audio analog-digital codecs, general analog to digital converter, battery charger, color led display drivers and backlights, touch screen interface, time of day clock and several power regulators to power these within. The MC13783 integrated circuit had several pin-programmable minimum startup sequences and other startup sequences directed by a system controller. The MC13783 integrated circuit startup sequences directed by the system controller included validation of battery voltage, verification of why power was requested, detecting which accessories were attached and configuration and startup of the power regulators. The system controller and software sometimes enabled some power regulators before others. The software specified a default state for regulators which may use either an internal pass device or an external pass device. A startup sequence was advantageous for power regulators because it minimized current consumption, since not all the regulators needed to be on by default. However, in this example of the art, care had to be used in defining the startup sequence to assure that the software for the system controller was correct and every circuit necessary for startup had an activated regulator.
FIG. 1 illustrates a schematic block diagram from the prior art where a power regulator capable of supporting internal or external pass devices was configured to use an external pass device 185 to power a load 189 from a battery or power supply 181. When in this mode, the interstage amplifier 115 was also enabled. To be used in this mode, a bus 190 provided a configure command from the bus 190. The configure command from the bus 190 needed to be set so that the external pass device 185 was actively driven, and the internal pass device 180 was not. FIG. 1 also illustrates differential amplifier 110, level select 120, output pulldown 130, not enable 135, inverter 193, and external bypass capacitor 187.
FIG. 2 illustrates a schematic block diagram of the same power regulator from the prior art to power a load 289 from a battery or power supply 281, but unlike in FIG. 1, an internal pass device was used. Note the configure command from the bus disabled the interstage amplifier, to save current, and routed the output of the error amplifier to the gate of the internal pass device. A bus 290 provided a configure command which needed to be set to actively drive the internal pass device 280 rather than an external pass device, and an interstage amplifier 215 was disabled. FIG. 2 also illustrates differential amplifier 210, level select 220, output pulldown 230, not enable 235, inverter 293, external bypass capacitor 287 and inputs 222, 222 and 223. One implementation in the prior art, the regulator, was part of the above-mentioned integrated circuit part number MC13783. Either the external pass device 185, as shown in FIG. 1, or the internal pass device 280, as shown in FIG. 2, was selected by switch 195 or 295 under control of a configure command on bus 190 or 290 from system controller 191 or 291.
The system controller 191 or 291 was a software based minicomputer or processor of its own integrated circuit separate and external to the integrated circuit of the regulator. An example of such processor was the MCIMX31 Multimedia Applications Processor by Freescale, Inc. The system controller was a separately packaged integrated circuit and separate from the MC13783 integrated circuit. This external system controller 191 and 291 was tasked with configuring a number of other devices within several other integrated circuits besides regulators. The system controllers were implemented with software by general microprocessors as well as combinations of microprocessors and digital signal processors (DSPs), generally referred to as baseband processors. The bus 190 or 290 carried many other commands to the integrated circuits to be controlled besides commands from the system controller 191 or 291 to the power regulator shown in FIGS. 1 and 2. Other circuits within the MC13783 integrated circuit were concurrently enabled or re-configured by the system controller 191 and 291 to minimize current drain.
The system controller 191, 291 usually accessed non-volatile memory (NVM), where software containing status for whether or not the external pass devices were part of the assembly was stored. If the particular regulator that has an internal or external pass device is needed as part of the power-up sequence, it may not have been appropriately configured at power-up.